The present invention relates to a method and system for energy conversion from pressure energy into electrical energy using an expansion turbine, wherein a pressurized, gaseous, first medium is heated before being fed into the expansion turbine and the expansion turbine drives a generator.
Within the scope of a growing increase in efficiency of processing plants or power plants, there is an increasing demand for making use of the high-pressure energy of resultant process gases, to use the process gases to operate generators, for example, for generating electrical energy. For this purpose, the process gas is fed to an expansion turbine or an expander which reduces the pressure in a controlled manner and converts the pressure into mechanical energy in the form of rotational energy. Because of the pressure reduction, the process gas cools down considerably due to the so-called Joule-Thomson effect. Ice crystals can form in this case during the use of process gases having a certain portion of residual moisture, for example, humid air or natural gas, when a limit temperature is fallen below, for example T=0° C. in the case of water. Due to the relatively high flow velocities in an expansion turbine, the ice crystals carried along in the flow can result in considerable damage, and therefore a formation of ice should be ruled out in advance.
A method has proven particularly successful in this case in which the process gas is heated, before being fed into an expansion turbine, in such a way that the expansion ensures that a lower limit temperature, at which ice crystals can form, is not fallen below. The heat source for the heating process is primarily the hot exhaust gas from a combustion system.
For example, DE 101 55 508 A1 describes a method in which pressurized natural gas is heated, before the expansion in an expansion turbine, by means of a branch flow from the water-steam circuit, which was previously heated in a waste heat boiler operated by the hot exhaust gases of a gas turbine.
According to EP 0 670 957 B1, the heat required for the heating process is obtained via a block-type thermal power station consisting of a gas internal combustion engine and a generator for power generation.
The problem associated with the previously utilized methods, however, is that heating the process gases always requires the use of combustion processes. This method is therefore not particularly efficient, either from an ecological perspective or from an economic perspective. Also, it is disadvantageous in this case that additional greenhouse gases are also emitted due to a classical burning of gas.